Top load socket for ball grid array devices

ABSTRACT

A test socket for temporary connection of a ball grid array integrated circuit device to a test circuit includes an array of contacts each including two cantilever arms biased toward each other and terminating in tips adapted to capture one ball of the device.

FIELD OF THE INVENTION

The present invention relates generally to sockets for the temporaryconnection of electronic devices to test circuitry, and, moreparticularly, sockets for ball grid array devices.

BACKGROUND OF THE INVENTION

Integrated circuit (IC) devices are finding wide-spread use in theelectronics industry and before they are bonded to a circuit the sameare tested to determine whether the IC device is functioning and thatelectrical continuity is present between the various portions of thedevice. To do this, the IC is placed in a socket which is attached totest circuitry. The whole assembly of test circuitry and IC may also besubjected to elevated temperatures while the IC is being electricallytested. Thus the procedure may be referred to as "test and burn-in" andthe socket a test and burn-in socket.

One type of IC device is formed merely with small balls of solderattached to one planar surface of the device in a regular array ofequally spaced rows and columns. Such a device is called a ball gridarray (BGA) device and is designed to be mated to an interface circuitboard by reflow soldering the BGA solder balls to an equal number ofpads on the circuit board.

Test sockets for BGA devices in the past have contacted the solder ballswith a single beam contact or a pointed rod contact which have causedundesirable damage to the solder balls or imparted unbalanced forces tothe BGA device which had to be countered by the structure of the socket.It would be desirable to provide a socket which eliminated theseundesirable effects.

SUMMARY OF THE INVENTION

The present invention improves upon existing BGA test sockets byproviding a contact for each ball which is comprised of two cantileverarms terminating in inwardly-bent contact tips. The arms are arranged tobe biased toward each other in the manner of a pair of tweezers. Sincethere are two contact arms, the forces on the contact balls of the BGAare balanced and thus no forces are transmitted to either the IC deviceor the socket structure supporting the contacts. Because the tips areinwardly bent, the balls are positively captured and the IC devicesecurely maintained within the socket.

In particular, the test socket of the present invention includes a baseof electrically insulating material, an array of contacts supported bythe base, the array at least including a pattern of contactscorresponding to the ball grid array of the integrated circuit device,each contact including a set of two cantilever arms biased toward eachother and terminating in tips adapted to capture one ball of the ballgrid array integrated circuit device, and means for simultaneouslyseparating each of the sets of the array of contacts so that the ballsof the ball grid array device may be inserted one within each of the setof contact arms.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more thoroughly described with respect tothe accompanying drawings, wherein like numbers refer to like parts inthe several views, and wherein:

FIG. 1 is a perspective view of a BGA test socket according to thepresent invention;

FIG. 2 is a perspective view of a pair of contacts designed for use inthe socket of FIG. 1;

FIG. 3 is a perspective view of a portion of the socket of FIG. 1illustrating the relationship between the contacts of FIG. 2 and the BGAIC device which is to be tested;

FIG. 4 is a perspective view, with a portion in cross-section, ofcontact actuating members of the test socket of FIG. 1;

FIG. 5 is a perspective view of the test socket of FIG. 1 with the coverremoved; and

FIG. 6 is a view similar to that of FIG. 5 with the test socket in aposition to accept a BGA device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a ball grid array (BGA) socket generally indicated as10. The socket 10 includes a base 12 of electrically insulatingmaterial, a cover 14 and an operating mechanism 16 disposed between thebase 12 and the cover 14. The cover 14 includes an opening 18 in theshape of the BGA integrated circuit device (not shown) with which thesocket 10 is to be used.

FIGS. 2 and 3 illustrate the contacts 20 disposed within the operatingmechanism 16 of the socket 10 which are designed to make an electricalconnection with the BGA device. Each contact 20 includes two cantileverarms 22 and 24 which terminate in tips 26 and 28 offset from each otherrelative to the direction of travel of the arms 22 and 24. The arms 22and 24 are of a resilient, highly conductive metal such as copper or analloy of copper, and so attempt to return to the position shown in FIG.3 when the tips 26 and 28 are spread apart. The contacts 20 furtherinclude a tail 30 for electrical contact to a circuit board or the like.

FIG. 2 shows the tails 30 of the contacts inserted through the base 12,with the contacts arranged in an array of rows and columns. Locatedbetween adjacent rows of contacts 20 are racks 32 having attachedthereto triangular projections 34 which engage the tip portions 26 and28 of the contacts 20. The racks 32 are connected at one end to a guide36 which moves with the rack 32 to move as will be described below. Itcan be seen in FIG. 2 that every other rack illustrated is connected toone of the guides 36 illustrated. This arrangement is such that everyother rack 32 travels in the same direction with intermediate racks 32traveling in the opposite direction. The direction of travel of twoadjacent racks 32 is indicated by the arrows 38.

It will be noted that the tips 26 and 28 of adjacent rows of contacts 20are offset in opposite directions, this allows one rack 32 withtriangular projections 34 on each side to operate on two tips 26, 28 oftwo rows of contacts 20 and so reduce the complexity of the mechanisminvolved.

FIG. 4 illustrates how the contacts 20 engage the solder balls 40 of aBGA device. The flat surfaces of the solder balls 40 indicate the planeat which the balls 40 are attached to the BGA device (not shown). As canalso be seen in FIG. 3, the tips 26 and 28 of the contacts 20 aretwisted toward each other so that the engagement surfaces of the tips 26and 28 are tangential to the solder balls. This arrangement allows amaximum area of the contact tips 26 an 28 to contact the balls 40 andprevents any gouging of the balls 40. The amount of twist necessary toresult in tangential engagement of the tips 26 and 28 and the solderballs 40 will depend upon the diameter of the balls 40. It will also benoted that the engagement portion of the tips 26 and 28 are bentinwardly where they engage the solder balls 40. This results in adownward force on the solder balls 40 which aids in the retention of theIC device within the socket 10.

FIGS. 5 and 6 illustrate the socket 10 with the cover 14 removed toexpose the operating mechanism 16 disposed within the socket 10. FIG. 5illustrates the mechanism 16 in a position wherein the contacts 20 wouldbe closed and thus would grip the solder balls 40 of a BGA device if onewere in place within the socket 10. FIG. 6 illustrates the mechanism 16in the open position wherein the contacts 20 are spread and ready toreceive the solder balls 40 of the BGA device.

The mechanism 16 includes two identical U-shaped brackets 42 and 44 eachhaving a formed cross piece 46 and two upstanding arms 48 and 50extending substantially perpendicular to the cross piece 46. The twobrackets 42 and 44 are nested facing each other and have their arms 48and 50 pinned to each other at approximately their midpoints with a holeand slot arrangement which allows the arms 48 and 50 of each bracket 42and 44 to slide relative to each other as the ends of the arms 48 and 50move up and down. The lower portions of the cross pieces 46 are pivotedwithin slots in the base 12 and the upper portions of the cross pieces46 engage the ends of the racks 32 which include the guides 36. Thedimensions of the brackets 42 and 44 are chosen such that the upperportions of the cross pieces 46 are forced apart, and thus the arms 48and 50 forced upwardly, when the contacts 20 are closed and thus theguides 36 are at their maximum separation. That the guides 36 are attheir maximum separation is illustrated by comparing the positions ofthe plate 52 which supports the guides 36 on the right side of thesocket 10 and the ends 54 of the racks 32 adjacent these guides 36. InFIG. 5, which corresponds to the closed position of the contacts 20,there is a large separation between the ends 54 of the racks 32 and theplate 52, which indicates that the guides 36 are at their widestseparation. In FIG. 6, which corresponds to the open position of thecontacts 20, the ends of the racks 32 have fully approached the plate52, indicating maximum travel of the racks 32 and thus full opening ofthe contacts 20.

To insert a BGA device in the socket 10, the cover 14 is depressed whichforces the ends of the arms 48 and 50 downwardly. This motion of thearms 48 and 50 causes the upper portions of the cross pieces 46 toapproach each other and thus force the guides 36 and their associatedracks 32 toward each other to open the contacts 20. The guides 36 arethen in a position to define the placement of the BGA device on the topof the racks 32.

Once the BGA device is placed between the guides 36, the solder balls 40attached to its bottom side are positioned within the open contacts 20and the socket 10 is ready to be closed. Releasing the downward pressureon the cover 10 allows the natural resiliency of the contacts 20 tocause the contacts 20 to close around the solder balls 40. At the sametime, the racks 32 are forced in opposite directions to fully separatethe guides 36. This action raises the arms 48 and 50 and thus the cover14.

Thus there has been described a test and burn-in socket for ball gridarray integrated circuit devices which uses two contact arms to gripeach solder ball of the device. Since two arms are used, forces arebalanced on the device and a large contact area per ball is definedwhich prevents damage to the solder balls.

Although the invention has been described with respect to only a singleembodiment, it will be recognized to those skilled in the art that manymodifications are possible. For example, the cover could be removedentirely and the arms actuated directly. In addition, the arms could belonger or shorter to require a greater or lesser travel of the cover.

I claim:
 1. A test socket for temporary connection of a ball grid arrayintegrated circuit device to a test circuit, the test socketcomprising:a base of electrically insulating material; an array ofcontacts supported by said base, said array at least including a patternof contacts corresponding to the ball grid array of the integratedcircuit device, each contact including a set of two cantilever armsbiased toward each other and terminating in tips adapted to capture oneball of the ball grid array integrated circuit device; means forsimultaneously separating each of said sets of said array of contacts sothat the balls of the ball grid array device maybe inserted one withineach of said set of contact arms.
 2. A test socket according to claim 1wherein said tips of said contacts are offset with respect to thedirection of movement of said tips and wherein said tips are twistedtoward each other to engage the balls over a maximum area.
 3. A testsocket according to claim 1 wherein said means for separating saidcontact tips includes a rack associated with each of said tips and meansfor forcing adjacent racks in opposite directions.
 4. A test socketaccording to claim 3 wherein said means for forcing said racks inopposite directions includes a linkage of two U-shaped pieces each of across piece and two upstanding arms, and wherein said arms are connectedsuch that pressure on said arms at a point distant from said crosspieces causes said cross pieces to approach each other, and wherein saidracks are disposed between said cross pieces and move with motion ofsaid cross pieces.
 5. A test socket according to claim 4 furtherincluding a cover including an opening for accepting a ball grid arraydevice and a surface contacting said arm ends to pressure said arms assaid cover is depressed and thus cause said cross pieces to approacheach other.
 6. A test socket according to claim 5 further includingmeans on said base and said cover for cooperatively guiding said coverwith respect to said base as said cover is depressed. .Iadd.
 7. A testsocket for temporary connection of a ball grid array integrated circuitdevice to a test circuit, the test socket comprising:a base ofelectrically insulating material; an array of contacts supported by saidbase, said array at least including a pattern of contacts correspondingto the ball grid array of the integrated circuit device, each contactincluding a set of two cantilever arms biased toward each other andterminating in tips adapted to capture one ball of the ball grid arrayintegrated circuit device; and an engagement member within said testsocket, said engagement member proximate said contacts to simultaneouslyseparate each of said sets of arms of said array of contacts when saidengagement member engages said contacts so that the balls of the ballgrid array device maybe inserted one within each of said set of contactarms. .Iaddend..Iadd.8. The test socket according to claim 7, whereinthe tips of the contacts are offset with respect to the direction ofmovement of the tips and wherein the tips are twisted toward each otherto engage the balls over a maximum area. .Iaddend..Iadd.9. A test socketaccording to claim 7, wherein the engagement member includes at leastone rack. .Iaddend..Iadd.10. The test socket according to claim 7,wherein the engagement member includes a plurality of racks, at leastone of the racks operating on a plurality of arms. .Iaddend..Iadd.11.The test socket according to claim 7, said socket further comprising atleast one bracket coupled to the engagement member, the bracketoperating as a lever such that pressure on the bracket causes theengagement member to move and separate the contact arms..Iaddend..Iadd.12. A test socket according to claim 7, wherein theengagement member includes a plurality of racks, the socket furthercomprising at least two brackets operating as levers for forcing theracks in opposite directions, the brackets including a linkage of twoU-shaped pieces each of a cross piece and two bracket arms, and whereinthe bracket arms are connected such that pressure on the bracket arms ata point distant from the cross pieces causes the cross pieces toapproach each other, and wherein the racks are disposed between thecross pieces and move with motion of the cross pieces..Iaddend..Iadd.13. The test socket according to claim 12, the socketfurther comprising a cover for accepting the ball grid array device, thecover coupled to the brackets to cause the cross pieces to approach eachother as the cover is depressed. .Iaddend..Iadd.14. The test socketaccording to claim 7, the socket further comprising a cover foraccepting the ball grid array device, the cover coupled to theengagement member such that the engagement member separates the contactarms when the cover is depressed and allows the arms to capture balls ofthe ball grid array when the cover is released. .Iaddend..Iadd.15. Thetest socket according to claim 7, the engagement member engaging atleast one arm of each of the contacts. .Iaddend..Iadd.16. The testsocket according to claim 7, the engagement member engaging both arms ofeach of the contacts. .Iaddend..Iadd.17. A socket for connection of aball grid array integrated circuit device to a circuit, the socketcomprising: a base; an array of contacts supported by said base, saidarray at least including a pattern of contacts corresponding to the ballgrid array of the integrated circuit device, at least some of saidcontacts including a set of two cantilever contact arms biased towardeach other and terminating in tips adapted to receive one ball of theball grid array integrated circuit device; and a sliding plate withinsaid test socket, said sliding plate adapted to separate said arms sothat a ball of the ball grid array device may be received within one setof said contact arms. .Iaddend..Iadd.18. The socket according to claim17, the socket further comprising a plurality of the sliding plates..Iaddend..Iadd.19. The socket according to claim 17, the socket furthercomprising a bracket coupled to the sliding plate, pressure on thebracket causing the sliding plate to move and thus separate the contactarms. .Iaddend..Iadd.20. The socket according to claim 19, the socketfurther comprising a cover for accepting the ball grid array device, thecover coupled to the bracket to cause the contact arms to separate whenthe cover is depressed. .Iaddend..Iadd.21. The socket according to claim17, the socket further comprising a cover for accepting the ball gridarray device, the cover coupled to the sliding plate such that thesliding plate separates the contact arms when the cover is depressed..Iaddend..Iadd.22. The socket according to claim 17, the sliding plateengaging at least one arm of each of the contacts. .Iaddend..Iadd.23.The socket according to claim 22, the socket being a test socket fortemporary connection of the ball grid array device to a test circuit..Iaddend..Iadd.24. A socket for connection of a ball grid arrayintegrated circuit device to a circuit, the socket comprising:a base; anarray of contacts supported by said base, said array at least includinga pattern of contacts corresponding to the ball grid array of theintegrated circuit device, at least some of said contacts including aset of two cantilever arms biased toward each other and terminating intips adapted to receive one ball of the ball grid array integratedcircuit device; and a rack within said test socket, said rack separatingat least one arm of each of said sets of arms so that at least one ballof the ball grid array device may be inserted within at least one ofsaid set of contact arms. .Iaddend..Iadd.25. The socket according toclaim 24, said socket further comprising a bracket coupled to the rack,pressure on the bracket causing the rack to move and thus separate thecontact arms. .Iaddend..Iadd.26. The socket according to claim 25, thesocket further comprising a cover for accepting the ball grid arraydevice, the cover coupled to the bracket to cause the contact arms toseparate when the cover is depressed. .Iaddend..Iadd.27. The test socketof claim 25, said socket further comprising a plurality of said racks,said racks being slidable to engage at least two arms of each of saidcontacts. .Iaddend..Iadd.28. The test socket of claim 24, said rackbeing slidable to engage one arm of each of said contacts..Iaddend..Iadd.29. The socket according to claim 24, the socket furthercomprising a cover for accepting the ball grid array device, the covercoupled to the rack such that the rack separates the contact arms whencover is depressed. .Iaddend..Iadd.30. The socket according to claim 24,the socket being a test socket for temporary connection of the ball gridarray device to a test circuit. .Iaddend..Iadd.31. A socket forconnection of a ball grid array integrated circuit device to a circuit,the socket comprising:a plurality of contacts within said socket, atleast some of said contacts including a set of at least two arms, saidarms terminating in tips adapted to receive one ball of the ball gridarray integrated circuit device; and a moveable engagement memberproximate said plurality of contacts, said member capable of separatingsaid sets of arms when said member is moved so that at least one ball ofthe ball grid array device maybe inserted within one of said sets ofcontact arms. .Iaddend..Iadd.32. The socket according to claim 31, saidsocket further comprising a bracket coupled to the engagement member,pressure on the bracket causing the engagement member to move and thusseparate the contact arms. .Iaddend..Iadd.33. The socket according toclaim 32, the socket further comprising a cover for accepting the ballgrid array device, the cover coupled to the bracket to cause the contactarms to separate when the cover is depressed. .Iaddend..Iadd.34. Thesocket according to claim 31, the socket further comprising a cover foraccepting the ball grid array device, the cover coupled to theengagement member such that the engagement member separates the contactarms when the cover is depressed. .Iaddend..Iadd.35. The socket of claim34, said engagement member being formed of multiple sub-members toslidably engage at least two arms of each of said contacts..Iaddend..Iadd.36. The socket of claim 34, said engagement member beingslidable to engage one arm of each of said contacts. .Iaddend..Iadd.37.The socket according to claim 36, the socket being a test socket fortemporary connection of the ball grid array device to a test circuit..Iaddend..Iadd.38. A test socket for temporary connection of a ball gridarray integrated circuit device to a test circuit, the test socketcomprising:a base; an array of contacts supported by said base, saidarray at least including a pattern of contacts corresponding to the ballgrid array of the integrated circuit device, each contact including aset of two cantilever arms biased toward each other and terminating intips to receive one ball of the ball grid array integrated circuitdevice; a moveable contact engagement member within said test socket,said contact engagement member proximate said contacts; a moveable coverhaving an opening for accepting the ball grid array device; and at leastone moveable bracket coupled to said contact engagement member and saidcover, said cover engaging said bracket when said cover is depressed,said bracket transmitting force to said engagement member tosimultaneously separate each of said sets arms when said cover isdepressed so that the balls of the ball grid array device may beinserted within the sets of said contact arms. .Iaddend..Iadd.39. Thetest socket of claim 38, further comprising a plurality of saidbrackets. .Iaddend..Iadd.40. The test socket of claim 38, wherein saidbracket is U-shaped. .Iaddend..Iadd.41. The test socket of claim 38,wherein at least one arm of each of said set of arms is moved toaccomplish said separation of said arms. .Iaddend..Iadd.42. The testsocket of claim 38, wherein one arm of each of said set of arms isengaged by said engagement member. .Iaddend..Iadd.43. The test socket ofclaim 42 wherein both arms of each of said set of arms are moveable..Iaddend..Iadd.44. A method of operating a test socket for temporaryconnection of a ball grid array integrated circuit device to a testcircuit, the method comprising:providing a base of electricallyinsulating material; providing an array of contacts supported by saidbase, said array at least including a pattern of contacts correspondingto the ball grid array of the integrated circuit device, each contactincluding a set of two cantilever arms biased toward each other andterminating in tips adapted to capture one ball of the ball grid arrayintegrated circuit device; and simultaneously separating each of saidsets of arms so that the balls of the ball grid array device may beinserted one within each of said set of contact arms. .Iaddend..Iadd.45.The method of claim 44, said separating step further comprisingdepressing a cover of said socket to actuate the separation of saidarms. .Iaddend..Iadd.46. The method of claim 45, wherein said coverpresses against a bracket when said cover is depressed..Iaddend..Iadd.47. The method of claim 44, said separating step furthercomprising: depressing a cover of said test socket to move at least onebracket within said test socket; and engaging at least one arm of eachof said sets of contact arms when said bracket is moved so as toseparate each of said sets of arms. .Iaddend..Iadd.48. A method ofoperating a test socket for temporary connection of a ball grid arrayintegrated circuit device to a test circuit, the method comprising:providing a base of electrically insulating material; providing an arrayof contacts supported by said base, said array at least including apattern of contacts corresponding to at least a subset of balls of theball grid array of the integrated circuit device, each contact includinga set of two cantilever arms biased toward each other and terminating intips adapted to capture one ball of the ball grid array integratedcircuit device; depressing a cover of said test socket to move at leastone bracket within said test socket; and engaging at least one arm ofeach of said sets of contact arms when said bracket is moved so as toseparate each of said sets of arms a distance sufficient to allow atleast one of the balls of the ball grid array device to be insertedwithin at least one of said set of contact arms. .Iaddend..Iadd.49. Themethod of claim 48, wherein depressing said cover moves a plurality ofbrackets. .Iaddend..Iadd.50. The method of claim 48, wherein saidmovement of said bracket actuates an engagement member to cause movementof at least one arm of each of said sets of contact arms..Iaddend..Iadd.51. The method of claim 48, said method furthercomprising placing a ball grid array device within said set of contactarms. .Iaddend..Iadd.52. The method of claim 51, said method furthercomprising releasing said cover to allow said contact arms to contactthe balls of said ball grid array. .Iaddend..Iadd.53. A method ofoperating a socket for connection of a ball grid array integratedcircuit device to a circuit, the method comprising: providing an arrayof contacts, at least some of said contacts including a set of at leasttwo arms, said arms terminating in tips adapted to receive one ball ofthe ball grid array integrated circuit device; and separating each ofsaid sets arms so that the balls of the ball grid array device may beinserted within said sets of contact arms. .Iaddend..Iadd. The method ofclaim 53, said contact arms being cantilevered to allow movement of atleast two arms of each set of arms. .Iaddend..Iadd.55. The method ofclaim 54, said separating step further comprising depressing a cover ofsaid socket to actuate the separation of said arms. .Iaddend..Iadd.56.The method of claim 55, wherein said cover presses against a bracketwhen said cover is depressed. .Iaddend..Iadd.57. The method of claim 53,said separating step further comprising:depressing a cover of said testsocket to move at least one bracket within said test socket; andengaging at least one arm of each of said sets of contact arms when saidbracket is moved so as to separate each of said sets of arms..Iaddend..Iadd.58. A method of forming a test socket for the temporaryconnection of a ball grid array integrated circuit device to a testcircuit, the method comprising: forming a base; and forming an array ofcontacts supported by said base, said array at least including a patternof contacts corresponding to the ball grid array of the integratedcircuit device, each contact including a set of two cantilever armsbiased toward each other and terminating in tips adapted to receive oneball of the ball grid array integrated circuit device;wherein each ofsaid sets of arms are separable so that the balls of the ball grid arraydevice maybe inserted within said sets of contact arms..Iaddend..Iadd.59. The method of claim 58, further comprising coupling acover to said socket so that actuation of the separation of said armsmay be accomplished by depressing said cover. .Iaddend..Iadd.60. Themethod of claim 59, further comprising coupling a moveable bracket tosaid cover. .Iaddend..Iadd.61. The method of claim 58, furthercomprising: coupling a cover of said socket to at least one bracketwithin said test socket so that depressing said cover moves saidbracket; and coupling said bracket to a slidable member, said slidablemember proximate at least one arm of each of said sets of contact armssuch that movement of said bracket may separate each of said sets ofarms when said cover is depressed and may allow closure of the arms whensaid cover is released. .Iaddend..Iadd.62. The method of claim 61, saidcontact arms being cantilevered to allow movement of at least two armsof each set of arms. .Iaddend..Iadd.63. The method of claim 58, saidcontact arms being cantilevered to allow movement of at least two armsof each set of arms. .Iaddend.